Field of the Invention
The present invention relates to a heat spreading module that is used for a portable electronic device such as a multifunctional mobile phone (smartphone) and a tablet personal computer.
Description of Related Art
A portable information terminal configured to transfer heat of a heating element to a low temperature portion by a heat pipe is described in Japanese Unexamined Patent Application, First Publication No. 2014-165596 A. The heat pipe is configured such that a copper tube is sealed at both ends thereof and a working fluid is contained inside the copper tube. A central portion of the heat pipe is arranged on an upper surface of the heating element, that is, a CPU, and both end sides extend to a battery side along a side portion of a casing. In the configuration described in Japanese Unexamined Patent Application, First Publication No. 2014-165596 A, the central portion of the heat pipe arranged on the CPU is a flattened portion processed flatly due to a restriction on the space such as a reduction in the thickness of the casing.
In an electronic device such as the portable information terminal described in Japanese Unexamined Patent Application, First Publication No. 2014-165596 A, the CPU mounted on a substrate (motherboard) has a greater height than other elements. When the flattened portion of the heat pipe is arranged on the CPU as described in Japanese Unexamined Patent Application, First Publication No. 2014-165596 A, therefore, the information terminal can be thinned. In the configuration described in Japanese Unexamined Patent Application, First Publication No. 2014-165596 A, however, almost all of the heat of the CPU is transferred to the heat pipe, and the heat pipe transfers that heat. The heat pipe thus requires a large heat transfer capacity, and there is no other choice but to use the heat pipe having a large size or a large diameter. Accordingly, the information terminal is increased in size or thickness.
In addition to the large amount of heat input from the CPU to the heat pipe, since a heat input portion (or heated portion) that receives heat from the CPU is the flattened portion, the amount of working fluid retained in the heat input portion is small. When the amount of heat generation in the CPU is large, therefore, dry-out of the heat pipe is likely to occur, whereby capability to cool down the CPU might be limited.